Can earth assimilate the additional 70 million tons of sulfur that we release each year? What happens to plants that absorb the additional nitrogen oxides (NOx) we create with our miniature lightning bolts inside car cylinders? Can the atmosphere take on the extra load of carbon dioxide (C02), methane, man-made ozone, and chlorofluorocarbon refrigerants that scientists say could raise global temperatures by the greenhouse effect?

Scientists worry that the growing burden of C02 and other gases may change earth's climate. Like panes of glass in a greenhouse, CO2 allows most solar radiation to penetrate the atmosphere (right, top) but prevents part of the heat reradiated by land and bodies of water from escaping into space (right, middle). As CO2 accumulates, enough heat may be trapped to gradually warm the atmosphere (right, bottom).
Researchers estimate that the earth's mean temperature could rise 1.5°C to 4.5°C (2.5°F to 7.5°F) by the middle of the next century if greenhouse gases continue to increase at the current rate. That would make the atmosphere warmer than it has been at any time during the past 100,000 years. Global rainfall patterns could shift, bringing heavy rains to previously arid regions such as the Sahel and droughts to productive farmlands such as the U.S. Midwest.
The impact could be even greater at the Poles, where mean temperatures might rise as much as 10°C (18°F). If the West Antarctic ice sheet melted, as it did during a previous period 120,000 years ago, ocean levels could gradualy rise as much as 15 or 20 feet, flooding many cities and farm regions.
So far there has been no clear evidence that a warming trend has begun. But scientists warn that the atmosphere would require thousands of years to recover from a mean global warmup of 1.5° to 4.5° C.